Hey Gadget...
Not sure what issues you're having with Amazon, as far as ranking or conversions go.
Honestly, I've never been one to use a cookie cutter theme for my websites.
I usually strip the blog of all sidebars, and use my own product related images within the blog posts to make sales.
A few years ago I came across a course called "Info Product Killer" and, whilst this course was promoting Amazon products using static html sites, I soon realized that the wordpress platform was easier to rank than static sites.
At the time, Kubrik was the most prevalent wordpress theme for any basic wordpress install.
So, I played around with firebug (firefox) to make the blog look like a regular site, and all my blogs to date have the same format.
Bear also in mind that, from a seo perspective, wordpress is definitely NOT user friendly.. most titles within the title tags <title></title>, leave spaces at the beginning of the keyword, i.e. <title> my keyword</title> instead of <title>My Keyword</title>
Now, there are a lot of schools of argument in terms of whether the former format is seo friendly or it doesn't matter... but for me, it matters.
Also, most themes only have the H1 tag within the header.php file, whilst the page.php and single.php files will have H2 tags only for each single blog post.
As for the title format of single pages, wordpress usually has it in this format - title of post >> title of blog, or permalink >> title of post >> title of entire blog.
I also tend to make my blogs show one page per post, instead of the continuous multiple posts per view (as is wordpress in its default state).
I could go on and on to elaborate what I've been up to, seo wise to optimize my blogs... but that's for another topic.
In short, it doesn't matter what theme you use, just make sure your onpage factors are optimized in such a way that the competition will be scratching their heads at what's under the hood of your theme.
Hope this answers some, if not all of your concerns.
Good luck.
Edited by Rainmak3r, 16 February 2012 - 22:24.